I had bad cyano and recently just got a new patch after 6 months. I started feeding too much I believe. How I get rid of it is I use red slime and a dose below the recommended tank size, cut lights down a hr, feed every 3rd day. Also if you use red slime, ramp up your skimmer to take some out.

As for clown goby, Im not sure why they say beginner fish. I had one and lost it because it stopped eating. I tried mysis and chopped it up for its small mouth but that only lasted so long before it got super lean and died.